tests: Copy stdlib tests from Kotlin/JVM

This patch copies Kotlin/JVM stdlib tests (libraries/stdlib/test)
excepting ones with explicit java dependencies. It also transforms
the tests to use them as box-tests.

backend.native/tests/external/stdlib/collections/CollectionTest/decomposeSplit.kt

@@ -0,0 +1,8 @@
+import kotlin.test.*
+import kotlin.comparisons.*
+
+fun box() {
+    val (key, value) = "key = value".split("=").map { it.trim() }
+    assertEquals(key, "key")
+    assertEquals(value, "value")
+}